Changes

Tutorial12: Shell Scripting - Part 2

12 bytes added, 08:24, 18 March 2021

→‎INVESTIGATION 2: ADDITIONAL LOOPING STATEMENTS

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER''').

# '''Add execute permissions''' for this shell script and '''run Bash shell script''' What do you notice? Does the output for this shell script differ from '''for-4.bash'''? Why? We now want to introduce you to the use of '''error-checking'''.

# Use the '''more''' command to view the previously-created Bash shell script '''~/if-5.bash''' (eg. more ~/if-5.bash) Take a few moments to re-familiarize yourself with this shell script # Run your shell script by issuing: .~/if-5.bash When prompted, enter a '''letter''' instead of a ''number''. What happens? Let's edit the '''for-5.bash''' shell script to perform '''error-checking''' to force the user to enter a numeric value between 0 and 100. '''NOTE:''' The '''while''' statement can be used with the '''test''' command (or a simple linux command or a linux pipeline command) for error checking. In our case, we will use a pipeline command with extended regular expressions. In order to loop while the result is TRUE (not FALSE), you can use the negation symbol (!) to set the test condition to the opposite. # Use a text editor like vi or nano to edit the text file called '''~/if-5.bash''' (eg. vi ~/if-5.bash) If you are using the nano text editor, refer to notes on text editing in a previous week in the course schedule.

# Add the following lines in your shell script IMMEDIATELY AFTER the read statement to prompt the user for a mark: while ! echo $mark | egrep "^[0-9]{1,}$" > /dev/null 2> /dev/null do    read -p "Not a valid number. Enter a mark (0-100): " mark done

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER''').

# Run your shell script by issuing: ./for-5.bash

# When prompted, enter a '''letter''' instead of a ''number''. What happens? Does the shell script allow you to enter an invalid grade like '''200''' or '''-6'''? Let's add an additional error-checking loop to force the user to enter a number between 0 and 100.

# Use a text editor like vi or nano to edit the text file called '''~/if-5.bash''' (eg. vi ~/if-5.bash)

# Add the following lines in your shell script IMMEDIATELY AFTER the PREVIOUSLY ADDED error-checking code block to force the user to enter a valid number: while [ $mark -lt 0 ] || [ $mark -gt 100 ] do    read -p "Invalid number range. Enter a mark (0-100): " mark done

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER''').

# Run your shell script by issuing: .~/if-5.bash

# When prompted, enter a '''letter''' instead of a ''number''. What happens? Does the shell script allow you to enter an '''invalid grade''' like '''200''' or '''-6'''? Let's reinforce '''math operations''' in a shell script (that you created in '''tutorial 10''') and then incorporate math operations within a loop.

# Use a text editor like vi or nano to create the text file called '''for-6.bash''' (eg. vi for-6.bash) If you are using the nano text editor, refer to notes on text editing in a previous week in the course schedule.

Msaul

Administrators

13,420

edits

CDOT Wiki β

Changes

Tutorial12: Shell Scripting - Part 2

CDOT Wiki ^β